Hi Harvey,
Once the spatterdock is established the grass carp won't totally destroy it. Like Bob said, put a cage around it and it will establish itself, and probably spread. Usually, Sweet-scented White Water Lilies (Nymphaea odorate) won't cause as many problems as spatterdock, and they produce a nicer flower. Both provide good habitat. If either of these grow outside the range that you want them in, you can spread Navigate or spray with Eagre + surfactant. However, don't plant them in the first place if you have a situation where they will spread rapidly, for example, shallow, silty, wind protected ponds.
Other plants that I would consider for small fish cover include: Water Celery (aka Eel Grass, Vallisineria americana), Pondweed species (Potamogeton), Coontail (Ceratophyllum demersum), Bulrush species (Scirpus), Water Buttercup species(Ranunculus), Pickerel weed (Pontederia cordata), Water Shield (Brasenia schreberi) and Muskgrass (Chara). All of these plants have their pros and cons. I would highly recommend that you read as much as you can about them before you plant. Also, consider control options ahead of time to make sure you can deal with the plant. I think the book Water, Weeds & Algae is available on this site, and it is a great one. Also, we have lots of plant info, including some treatment tips, on our site.
